Coded track circuit system involving highway crossing signal control



R. M. LAURENSON CODED TRACK CIRCUIT SYSTEM INVOLVING HIGHWAY CROSSINGSIGNAL CONTROL Flled March 19 1946 June 20, 1950 INVENTORHaber/Mlaapmmzz.

Patented June 20, 1950 CODED TRACK CIRCUIT SYSTEM IN- VOLVING HIGHWAYCROSSING SIG- NAL CONTROL Robert M. Laurenson, Verona, Pa", assignor toThe Union Switch & Signal Company, Swissvale, Pa., a corporation ofPennsylvania Application March 19, 1946, Serial No. 655,635

7 Claims. (Cl. 246-130) My invention relates to railway signalingapparatus, and has particular relation to coded track circuit systems ofrailway signaling of the type in which approach functions are controlledthrough the medium of current transmitted through the traffic rails.More particularly, my invention relates to coded track circuit systemsof the type described incorporating means for providing a clearing outcontrol of such approach functions.

An object of my invention is to provide novel and improved railwaysignaling systems incorporating means for controlling approachfunctions. 7

Another object of my invention is to provide novel. and improved railwaysignaling systems incorporating improved means for obtaining clearingout controls of approach functions.

Another object of my invention is to provide novel and improved meansfor supplying both feed-back and clearing out code in a track circuitfor controlling approach functions.

Another object of my invention is to provide in a coded track circuitsystem of railway signaling, means for supplying the track rails of asection with code having similar characteristics both when such code isgenerated by the feedback principle in response to the receipt of mastercode, and when the code is locally generated as a supplemental clearingout code.

The above-mentioned and other important objects and characteristicfeatures of my invention are obtained by energizing the impulse relay atthe entrance end of a section through a transformer both when operatedon feed-back code and when operated on special supplemental code 10-cally generated, by providing means at the exit end for reversiblyoperating the polarized track relay at that end when clearing out codeonly is applied to the track rails, and by providing other novel andimproved apparatus described in detail in the accompanyingspecification.

I shall. describe one form of apparatus embodying my invention, andshall then point out the novel features thereof in claims.

The accompanying drawing illustrates a preferred embodiment of myinvention represented in connection. with the control of an approachfunction constituting a highway crossing protective device.

Referring to the drawing. the reference characters L and fa designatethe traffic rails of a stretch of railway track over which traflicnormally operates in a given direction as indicated in. the drawing byan arrow, or from leit to right as viewed in the drawing. The trackrails l and la are divided by insulated joints 2 into a plurality ofsuccessive adjoining track sections, of which only one section, D-F, isshown in the drawing. Section D-F is further divided by insulated joints2 located at E into adjoining subsections DE and E-F, and as indicatedin the drawing, subsection D-,E is intersected at grade by a highway Hat the exit end of that subsection. Located at the intersection ofhighway H and the stretch is a highway crossing protective device XSwhich may take any one of a number of suitable forms, but which isillustrated for the sake ofsimplicity as a highway crossing bell. Thebell XS is normally deenergized but is supplied with energy over anobvious circuit whenever back contaot 41 of a relay EVM is closed.

The stretch of track is provided with a coded track circuit system forcontrolling signals, such as signal DS located at D, located along thestretch at the entrance of each section for governing the movement ,oftrafiic in the associated section, and also for controlling approachfunctions. The coded track circuit system of signaling provided forsection DF comprises master code transmitting means and approachfunction control means located at section end F, master code repeatingor cascading means and approach function control means provided atlocation E, and master decoding means and approach control codetransmitting means located at entrance end D of the section.

The apparatus at section end F comprises a transmitting relay FCTM, atwo-winding stick polar relay FVR, and an oscillation detecting relayFVM controlled by relay FVR. through the medium of a transformer It. Oneportion of primary winding II .of transformer i0 is supplied withunidirectional current from a suitable source indicated conventionallyin the drawing by the reference characters B and .C, when contact [3 ofrelay FVR. is in its left-hand position as illustrated in the drawing,and the other portion of winding ll of transformer It is supplied withunidirectional current when contact E3 of relay FVR. is operated to itsopposite or right-hand position. The mid terminal tap. ,of secondarywinding l2 of transformer I0 is connected to one terminal of relay FVMand the opposite end terminals of winding 12 are alternately connectedto the other terminal of relay F-VM according as contact M of relay FVRis in its left-hand or right-hand position, the arrangement being suchthat alternating current of relatively low frequency is induced insecondary winding ii of tween its left-hand and right-hand positions,but. when relay FVR maintains its polar contact con-"" stantly in eitherof its positions, the 'supplyof'v energy to relay FVM is thendiscontinued and-= that relay releases.

The transmitting relay FCTM is controlled over a circuit which may, forexample, be similar to the circuit hereinafter traced for thecorresponding transmitter relay DCTM, and is energized periodically atone or another of a plurality of code rates, preferably '75 or 180cycles per min-g ute, to operate its contacts and. 2| at thecorresponding rate alternately between front and back positions. ContactId of relay FCTM in its front position connects a battery FB to thetrack rails in series with winding I6 of a transformer l1 and resistorI9, thereby applying to the track rails an impulse of energy. whilecontact [5 of relay FCTM in its back position disconnects battery FBfrom the track rails and connects one winding of the two-winding stickpolar relay FVR to the rails. Contact 2| of relay FCTM in its frontposition connects a battery 22 in circuit with the other winding 23 ofrelay FVR and this battery is poled to energize'the relay in adirectionto cause it to operate its polar armature to its left-hand position. Therelay FVR is of the stick polar or stay-where-put type arranged to holdits polar armature in its last operated position.

The track circuit current intermittently applied to the rails of sectionEF each time front contact l5 of relay FCTM is closed, is transmittedthrough the track rails to the intermediate location E to effectenergization of track relay ETR located at that point. This trackcircuit current I shall term the ,master code. Track relay ETR hasassociated therewith a decoding transformer EDT, a. code detecting relayEH, and an impulse relay EIR. Front contact 25, of relay ETR suppliesone portion of primary winding 26 of transformer EDT with unidirectionalcurrent, and

back contact of relay ETR supplies unidirectional current to the otherportion of winding 25 of the transformer. One secondary winding 2! oftransformer EDT is connected with code detecting relay EH through themedium of contact 28 of relay ETR with the circuit connections beingarranged so that relay EH is supplied with unidirectional current whenthe armature of relay ETR operates alternately between its released andpicked-up positions, but relay EH becomes deenergized when the armatureof relay ETR remains continuously picked up or released, respectively.Another winding 29 of decoding relay EDT is connected to primary winding30 of a transformer 3| which has its secondary winding 32 connected tothe terminals of impulse relay EIR. Relay EIR is of the polar biasedtype responsive only to current of a preselected polarity and the partsare so arranged that transformer winding 29 cooperates with transformer3! to supply an impulse of current of the preselected polarity to relayEIR, each time back contact 25 of relay ETR closes. Relay EIR controls acontact 33 which when closed in its back position connects relay ETR tothe track rails, and which contact 33 when picked up disconnects relayETR 4 from the track rails and connects a battery EBF' in series withthe resistor 34 across the track rails. This connection of relay EBF tothe track rails when front contact 33 of relay EIR is closed, iseffective to transmit energy, which I shall term a feed-back code,through the track rails to the other end F of the section for supplyingwinding 20 of the two-winding stick polar relay FVR at that locationwith current having a polarity 'efi'ective to cause the relay to operateits polar armature from its left-hand position to its righthandposition, as Will be pointed out in more detail hereinafter.

' When relay ,ETR is following impulses of master code energy receivedfrom track rails l and la of subsection E-F, impulse relay EIR will besupplied with an energy impulse of the proper polarity to pick up thatrelay, only upon the release of relay ETR so that relay EIR picks up todisconnect relay ETR from the track rails only during the interval thatrelay ETR is released due to the off period of the master code energy inthe track rails, and it follows that the supply of feed-back code energyto the track rails from battery EBF is in step with the supply of energyto relay E'IR andis provided during the off period of the master code inthe section. The arrangement of transformer winding 29 and transformer3i operates to supply relay EIR with a relatively short pulse of energyof the predetermined polarity so that relay EIR has a very short ontime, that is, it will maintain its front contact 33 closed for arelatively short time which insures that the relay will release to closeits back contact 33 and connect relay ETR to the track rails prior tothe start of the next on time of the master code supplied at theopposite end of the section.

The apparatus at location E also includes a, two-winding polar stickrelay EVR, an oscillation detecting relay EVM controlled by relay EVR ina manner corresponding to that pointed out in detail whereby relay FVMis controlled by relay F'VR at location F, and another relay EVRAenergized whenever contact 35 of relay EVR is in its left-hand positionas indicated in the drawing. The circuit for relay EVRA extends fromterminal B through contact 35 of relay EVR in its left-hand position,asymmetrical unit 36 in its low resistance direction, and the winding ofrelay EVRA to terminal C, with resistor 31 and condenser 38 connected inmultiple with the winding of relayEBRA to provide slow releasecharacteristics to this relay. Relay EVRA controls a circuit for winding46 of relay EVR, passing from terminal B through back contact 39 ofrelay EH, the winding 46 of relay EVR, and back contact 49 of relay EVRAto terminal C, with the polarity of current selected to cause relay EVRto operate its polar armature to its left-hand posi- 'master code energyas long as front contact 40 of relay ETR remains picked up, andenergizing winding 45 of relay EVR with energy of a polarity such thatthe relay operates its polar armature to its left-hand position. Contact40 of relay ETR when released disconnects battery EBD from the trackrails to terminate the on pe.

rlod of the master code impulse while maintaining the connection ofwinding 45 of relay EVR to those rails, thereby preparing a circuitwhereby winding 45 may be energized by energy transmitted through thetrack rails from the entrance end D of the section.

The impulse of master code energy applied from battery EBD- to the trackrails of section D-E-each time contact 40 of relay ETR is closed in itsfront position is transmitted through the track rails when subsectionD-E is vacant to the entrance end D for operating a track relay DTRlocated at that point. Relay DTR has associated therewith a decodingtransformer DDT, a code detecting relay DH energized through the mediumof transformer DDT in a corresponding similar manner to that explainedin detail whereby relay EH is controlled by relay ETR throughtransformer EDT, a code discriminating relay DD energized throughtransformer DDT and a tuned circuit involving a condenser 56 with thecircuit proportioned to effectively energize relay DD when and only whenrelay DTR operates in response to 180 code in the track rails, and animpulse relay DIR biased to respond only to current of a preselectedpolarity. Relay DIR has its terminals connected to the secondary windingof a transformer 52 which in turn has its primary winding 53 connectedto secondary winding 54 of transformer DDT over front contacts 55 and 5Bof relay DH, but when relay DH is deenergized and contacts 55 and 53close to their back points, Winding 53 of transiformer 52 is thensupplied with unidirectional energy over contact 51 of a coding device150T. The arrangement is such that when relay DH is picked up relay DIRis supplied with one pulse of current, having a polarity selected tocause operation of the relay, each time that relay D'IR releases toclose its back contact 58, and when relay DH is released to close itsback contacts 55 and 5B, relay DIR is likewise supplied with an impulseof current of the proper polarity each time contact 5'! operates fromits front to its back position. It will be noted that the energizationof relay DIR is effected through the medium of transformer 52 both whenthe impulse originates in secondary winding 54 of transformer DDT andwhen the impulse originates through the closing of contact. 51 of thecode originating means CT. In each [0358, therefore, the impulse ofenergy that is induced in secondary winding 5| of transformer 52 will besubstantially identical because it is the result of the supply of energyto winding 53.

Relay DIR operates a contact 50, which when closed in its back positionconnects the track relay DTR across the track rails to receive mastercode energy over the track rails from exit end E of the subsection.Contact 60 when picked up disconnects relay DTR from the track rails andconnects a battery DB in series with resistor 6! across the track rails,with the battery poled in such a manner as to supply feed-backcodeenergy having a polarity such as to energize winding 45 of relay EVR-andoperate the polar armature of that relay to its right-hand position.When relay DTR is following impulses of master code energy received fromthe track rails i and la, of subsection D-E, impulse relay DIR operatesin the manner described with reference to relay EIR to apply impulses offeed-back code to the rails of the subsection during each off period ofthe master code in the subsection.

6, The-decoding relays DH and DD associated with relay DTR cooperate inthe usual manner to control signal DS located at the entrance end ofsection DF. This signalDSmay take any desired form but is represented asa color light signal. Control of. signal DS as shown is established whenboth relays DH and DD are picked up, through a circuit passingfromterminal B through front contact 62 of relay DH, front con! tact [i3 ofrelay DD, and the filament of lamp G of signal DS to terminal B; whenrelay DD is released'butrelay DH is picked up, the circuit passesfrom-terminal B through front contact 62 of relay DH, back contact 63 ofrelay DD and the filament of lamp Y of signal D8 to terminal B; and whenboth relays DH and DD are re leased, lamp R of signal DS is energizedover an obvious circuit including back contact 62 of re lay DH.- a YRelay DH also controls the energization of code transmittingrelay DCTMprovided for the section in the rear of section DF. This control of thetransmitter relay is established through a circuit for the winding ofrelay DCTM passing either through contact 64 of coding device 1323GT(which operates its contacts alternately between front and backpositions at the rate of I 180 times per minute) and front contact 65 ofrelay DH, or through contact 65 of coding device 750T (which operatesits contacts alternately between front and back positions at the rate oitimes per minute) and back contact 55 of relay DH. It isreadily apparentthat when section D-F is unoccupied so that the relay DH is-picked up,the transmitter relay is'then energized periodicallyat the rate of codepulses per minute, but that when section D'r' is occupied so that relayDH is released, relay DCTM is then ener gized periodically at a rate ofi5 code cycles per minute. The devices IHBCT and lBCT are arranged sothat front contact t t of lfltCT is closed for an intervalequalto theinterval that contact 64 is in its back position, and likewise contact[56 (and 51) of 'EBCT is closed in its front position for an intervalequal to the m terval that contact 66 (and El) occupies its backposition. This results in the generation of a master code in which theon intervals of the 180 code are equal in duration the off intervals'ofthat code,- and the on intervals of the 75 code are equal in duration tothe off intervals or that code.

Inorder to describe the operation of the apparatus set forth above, Ishall assume that the section in advance of section D-F is unoccupied sothat transmitter relay FC'IM at location F is energized periodically atthe rate of 180 code pulses per minute, and shall also assume thatsection D-F is unoccupied. Under these conditions, the apparatus of myinvention will be in the condition illustrated in the drawing. In thiscondition, relay. FCTM alternately opens and closes its contacts I5 andH at the rate of 180 times per minute to intermittently energize winding23 of relay FVR and provide 180 master code energy in the rails ofsubsection E-F. This current in the track rails operates relay ETR at acorresponding rate and as a result relay EH is picked up. Also, theoperation of relay ETR results in the operation of relay EIR at asimilar rate with the result that during the ofi period of each pulse ofmaster code in subsection E-F, feedback code supplied at E istransmitted through the track rails to end F where it energizes winding.20 of relay EVR, The alternate energization oi winding 23 of relay FVRby current from battery 22 having polarity such as to operate the relayarmature to its left-hand position, and of winding 20 of relay FVR.with'current from battery EBF having a polarity suchas to cause therelay to operate its armature to its right-hand position, results inrelay F'VM being picked up.

At location E of section D-'-F, the operation of relay ETR. at the 180code rate results in the operation of its contact 40 between its frontand back positions at a rate of 180 code pulses per minute, with theresult that 180 master code is repeated from section E-'F into the railsof section D-E. This 180 code pulse current is transmitted through thetrack rails to the entrance end D of the section where it operates relayDTR at the corresponding code rate, and relays DD and DH are picked up.Also, relay DIR at location D is energized at the 180 code rate to applyenergy impulses of feed-back code from battery DB to the track rails ofsubsection D-E each time an off interval occurs in the master codeapplied to subsection D-E and this feed-back code applied from batteryDB is transmitted through the track rails to exit end E where itenergizes winding 45 of relay EVR. The energization of winding 45 ofrelay EVR alternately by current from battery DB having a polarity tooperate the polar armature of the relay to its right-hand position, andby current from battery EBD having a polarity to operate the polararmature of the relay to its left-hand position, results in theenergization of repeating relay EVM. Also, relay EVRA is picked upbecause of this reversible operation of relay EVR, the slow releasingfeatures of the relay serving to maintain the relay picked up during theintervals that contact 35 occupies its right-hand position.

At entrance end D of the section, the energization of relays DH and DDresults in illumination of lamp G of signal DS to indicate clear trafiicconditions in the section, while transmitter relay DCTM is energized atthe 180 code rate and will function in the ordinary manner to apply 180,code rate pulses to the rails of the section in the rear of sectionD-F.

If a train operating in the stretch in the normal direction of traincenters section DF, the energy impulses supplied to the rails ofsubsection D--E at E are then shunted by the train wheels and axles awayfrom relay DTR, whereupon that relay releases and maintains its contactsin their back positionsso that relays DH and DD also release. Thiscauses signal DS to display its red aspect R, and also shifts theenergization of transformer 52 from winding 54 of transformer DDT tocontact 51 of coding device lCT. Relay DIR thereupon operates at the '75code rate, and battery DB is alternately connected to and disconnectedfrom the rails of section D-E at the rate of 75 times per minute, butthe energy applied at this time from battery DB to the track rails isshunted away from relay EVR by the train wheels and axles. This codedenergy differs from the feed back code previously mentioned because itis not generated in response to operation of relay DTR by master codeenergy, but is locally generated by coding device 15CT. This locallygenerated code I shall term a clearing out code.

At location E of section D-F, relay ETR continues to operate its contact40 at a rate corresponding to the code rate of the current in the railsof subsection D,F, with the result that code pulses. oi energy arecontinuously-applied to thexrails of. subsection DE, but as pointed outhereinbeforeqthis energy is 1 shunted away from relay DTR; Theconnection of battery EBD to the track rails energizes winding 45 ofrelay EVR with current "having a polarity effective to operate the relayarmature to its left-hand position, and since no energy from battery DBis transmitted through the track rails to winding 45 of relay EVR, thepolar armature of that relay remains in its left-hand position.

The polarized relay ENE at location E now ceases to operate its contactalternately between its left and right-hand positions and as a resultrelay EVM releases to close its back contact 41 and complete an obviousenergizing circuit for crossing signal XS which now becomes active toindicate to highway users that a train is approaching the intersection.Contact 48 of relay EVM may also close to complete an obvious circuitfor primary winding 43 of transformer 42, this winding being energizedfrom a suitable source of alternating current conventionally indicatedin the drawing by the reference characters BX and OK. The energizationof winding 43 causes the induction of alternating current in winding 4|and the intermittent connection of this winding to the track railsthrough front contact 40 of relay ETR. supplies coded alternatingcurrent to the track rails which may be utilized for controlling traincarried brake control or cab signal apparatus on the train.

When the train enters subsection D-F, relay ETR becomes shunted andoperates its contacts to their back positions, so that relay EH releasesto close its back contact 39 and prepare the energizing circuit forwinding 46 of relay EVR. Winding 45 of relay EVR is now constantlyconnected to, and battery EBD is disconnected from, the rails ofsubsection D-E. At the opposite end F of the subsection, the two-windingrelay FVR ceases to operate its contacts alternately between theleft-hand and right-hand positions, due to the fact that relay EIRremains released to out 01f battery EBF from the rails of section EF,and as a result approach control relay FVM releases to close its backcontact 24 to connect a source of alternating current to winding [8 oftransformer I1. This results in the induction of alternating current inwinding I6 and the alternate connection of this transformer winding tothe track rails supplies alternating current at the code rate to therails which may be used to control train carried apparatus.

When the train clears highway H and vacates subsection D--E, theclearing out code intermittently applied to the track rails from batteryDB each time relay DlRcloses its front contact 50 is transmitted throughthe track rails to location E where it energizes winding 45 of relay EVRwith current having a polarity effective to operate the polar armatureof that relay to its righthand position. This operation deenergizesrelay EVRA which thereupon releases to close its back contact 49 andthereby complete for winding 46 the previously traced circuit effectiveto energize that winding with current having a polarity such as tooperate the polar armature of relay EVR to its left-hand position.Operation of contact 35 of relay EVR to its left-hand position energizesrelay EVRA whereupon that relay picks up and opens its back contact 49to deenergize winding 46 of relay EVR, so that the next succeedingimpulse of clearing out code energy supplied over the track rails towinding 45 is effective to operate the polar armature of relay EVR toits right! hand position. This cycle of operation is maintained as longas relay EH is released, and results in relay EVR operating its contactsalternately between their left-hand and right-hand positions so thatrelay EVM becomes energized and opens its back contact 4'! todeenerg-ize the crossing signal XS and thereby terminate operation; ofthat signal. Also, back contact 48 of relay EVM opens to deenergizewinding 43 of transformer 42.

After the train vacates section D'F, '75 master code current is thenapplied at end P to the rails of subsection and. is repeated by relayETR into subsection D--E to cause relay DTR to operate at the 75 coderate and pick up relay DH to shift the energiz ation of relay DIR totransformer DDT and thereby restore the feed-back code. .Intermeshing ofthe independently generated 75 master code, supplied at E to rails l andla of subsection D-E, and '75 clearing out code supplied to the railsatD, is rendered impossible because of the different characteristics ofthe two codes. The master code is characterized by alternate on. and offintervals of substantially equivalent durations, while the clearing outcode consists of on intervals of very short duration separatedbyrelatively long duration off intervals. Should the first impulse of75- master code occur at the same time as an on interval of the clearingout code, both contacts 40 of ETR and 6B of DIR might be closed in theirfront positions, and both relay DTR and winding 29 of FVR might bedisconnected from'the track rails, but the short on time of relay DIRwill result in the release of that relay while front contact of ETRremains closed, so that relay DTR will be supplied with a portion of theon impulse of the 75 master code and will pick up to energize relay DH.and shift the energization of transformer 52 to winding 54 oftransformer DDT. Although both the clearing out w and, master codesappliedto the rails of subsection D- -E are independently generated bycontacts of 75 code generators which have equal on and off contacttimes, theclearing out code is provided with the distinctive short ontime characteristics through the use of transformer 52in the circuitover which contact 51 of coder TECT supplies energy to relay DIR). Theuse of thistransformer results in reducing the interval that energy ofthe preselectedpolarity is supplied to relay DIR,

from the relatively long on period that contact 5! of device 150T isclosed, to the relatively short period requiredior-the flux in thetransformer toreach a steady state condition (thus terminating inductionof energy in secondary winding 51) following operation of contact 51.

The picking up of relay DH inresponse'to operation of relay DTR bymaster code results in closing the 180 code energizing circuit for thecode transmittingrelay in closing the circuit for lamp Y of signal DS,-and in shifting the energization of winding 53 of transformer 52, fromback contact 51 of coding device HGT, to winding 54 oftransformer DDT sothat impulse relay DIR operates in synchronism with the oporation ofrelay to apply feed-back code impulses at the i5=code rate to the trackrails of section DE duringeach off period of the master code energyapplied to those rails for operation ofthe track relay DTR. Theoperation ofrelay ETR, at location E also results in the energization ofrelay EH so that the circuit for winding 46 of relay .EVR is opened atback contact 38 of relay EH, but relay EVR is now caused to operateitscontacts alternately between their left-handandright-hand positionsdue to the energization of winding .45 of that relay alternately byenergy from battery EB D and battery DE. The reversible operation of thecontacts of relay EVR maintains relay EVM picked up to deenergize theapproach control functions such as the highway crossing signal KS andtransformer 42. In addition, the two-winding stick polar relay FVRatlocation F is similarly reversibly operated by the energy suppliedalternately from batteries 22 and EBF so thatrelay FVR operates itspolar contacts alternately between their left and right-hand positionsto cause relay FVM to pick up and open itsback contact 24 to deenergizewinding [8 oftransformer 11.

'When the train clears the section in advance of the exit end F ofsection D-F, code transmitting relay FCTM is then caused to operate atthe code rate to cause operation of relays ETR and DTR at the same rate,whereuponrelay DD at location D becomes energized; the green lamp ofsignal DS becomes illuminated; and the apparatus is restored to thenormal condition as illustrated in the drawing.

It is to be noted that my invention is applied to the control of a stickpolar relay used as an approach code detecting relay in coded trackcircuit signaling systems provided with reverse or feed-back codes toobtain control of approach functions. The invention provides a novel andimprovedmeans in such systems, for obtaining a clearing out controliofthe approach functions to terminateoperation of a highway crossingSig-.- nal after atrain vac'ates a highway intersection.

The principle .of using a transformer in the circuit .forthe impulserelay energized by the locally operated generator, thereby to providedistinctive characteristics for the clearing out code which functions to.prevent the intermeshing of the clearing-out and master codes despitethe use of the same rates for the two codes, may of course beused-infeed-back coded trackcircuits incorporating feed-back operatedtrack relays of a-type different from the two-winding polar stick typeillustrated. For example, this principle may be used where the feed-backcode operated relay is of the single winding type and the circuit ar:rangement for connecting this relay .to the track rails is-similar tothat shown in Letters Patent of the United States No. 2,213,186, grantedto Herman G. Blosser on September 3, 1940, orin other arrangements suchas those making use of a polar biased relay such asis shown for exampleinv an application for Letters Patent of the United States SerialNo.452,983, filed by Howard A. Thompson on July 31,,1942,.now U. S.

Patent 2,401,201. r

Although I have herein shown and described only one form of apparatusembodying my invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of my invention. I

Having thus described my invention, what I claim is: 1 I I 7 1,111combination with a stretch of railway track over which traific operatesin onedirection and having an insulated track section, a source ofdirect current,-a two-winding stick polar re-' la, and a coding contactcontinuously operated between a first and a second position when thestretch in advance of said section is vacant, a circuit including saidcontact in its first position connecting said source and one winding ofsaid tw -w ndi r lay in s r s with th ails at which traflic operates inone direction and having end of said section for applying energy to saidrails and for operating the polar armature of" said two-winding relay toone of its two extreme positions, a, circuit including said contact inits said second position for disconnecting said source from said railswhile maintaining the connection of said one winding of said two-windingrelay to the rails at said one section end, means at the opposite end ofsaid section effective when said section is vacant and followingoperation of said coding contact from said first to said second positionfor supplying an impulse of energy to the rails at that section end,said impulse of energy having a polarity selected to cause operation ofsaid polar armature of said two-winding relay to its other of said twopositions, other means effective when said coding contact remainscontinuously in said second position for periodically supplying currentof said selected polarity to the rails at said opposite end, meanseffective when said polar armature of said two-winding relay i in itssaid other position and said coding contact remains continuously in saidsecond position for energizing the other winding of said two-windingrelay with energy having a polarity such as to cause the polar armatureof said two-winding relay to operate to its said one position, andcontrol means governed by the arma ure of said two-winding relay.

2. Highway crossing signal control apparatus for a coded track circuitsystem of railway signalin provided for a stretch of railway track overwhich traffic normally operates in a given direction and including aninsulated section of railway track intersected at its exit end by ahighway, said system having at said exit end a source of direct current,a two-winding polarized stick relay, and a coding contact continuously oerated between a first and a second position when the stretch in advanceof said section is vacant, a circuit including said contact in its saidfirst position for connecting said source and the one winding of saidtwo-winding relay in series with the rails of said section for applyingenergy to said rails and for operating the polar armature of saidtwo-winding relay to one of its two extreme positions, a circuitincluding said contact in its said second position for disconnectingsaid source from said rails while maintaining the connection of said onewinding of said two-winding relay to the rails, said system having atthe entrance end of said section means effective when said section isvacant and following each operation of said coding contact from saidfirstto said second position for supplying an impulse of energy to therails at that section end, said impulse of energy having a polarityselected to cause operation of said polar armature of said twowindingrelay to its other of said two positions. other means effective whensaid coding contact remains continuously in said second position forperiodically supplying current of said selected polarity to the rails atsaid entrance end, means effective when said two-winding relay operatesits polar armature to said other position and when said coding contactremains continuously in its said second position for supplying the otherwinding of said two-winding relay with energy having a polralityeffective to cause operation of the armature of said two-winding relayto its said one position, and highway crossing control means governed bythe operation of said armature of said two-winding relay.

3. In combination with a railway track over an insulated track section,a source of direct current, a two-winding polarized stick relay, and acoding contact at the exit end of said section, said coding contactcontinuously operating between a first and a second position when thestretch in advance of said section is vacant and efiective in said firstposition for connecting said source and one winding of said two-windingrelay in series with the rails of said section for applying energy tosaid rails and for operating the polar armature of said two-windingrelay to one of its two extreme positions and effective in the secondposition of said contact for disconnecting said source from the railswhile maintaining the connection of said one winding of said two-windingrelay to the rails, a track relay and an impulse relay responsive onlyto current of a selected polarity at the entrance end of said section, atransformer having its secondary connected to said impulse relay, acircuit for inducing in the secondary winding of said transformercurrent of said selected polarity to cause operation of said impulserelay each time said track relay releases and controlled by said trackrelay, another circuit controlled by said track relay for inducing inthe transformer secondary periodically interrupted current of saidselected polarity when said track relay ceases to follow code in saidtrack section, means controlled by said impulse relay for alternatelyconnecting said track relay and a source of current to the track railsat said entrance end of said section with said track source poled tosupply current having a polarity to cause operation of the polararmature of said twowinding relay at said exit end to its otherposition, means eflective when current is applied at the entrance end ofsaid section while said coding contact remains in its said secondposition for energizing the second winding of said two-winding relaywith current having a polarity to cause operation of said armature ofsaid twowinding relay to its said one position, and control meansoperated by the armature of said twowinding relay.

4. Highway crossing signal control apparatus for a coded track circuitsystem of railway signaling provided for a stretch of railway track overwhich traflic normally operates in a given direction and including aninsulated section of track intersected at grade by a highway, saidinsulated section subdivided by insulated joints at said intersectioninto adjoining front and rear subsections, said system including meansat the exit end of said front subsection for applying to, the trackrails thereof coded track circuit current comprising alternate on and onintervals during which respectively current is and is not supplied .tothe track rails and a track relay at the entrance end of said frontsubsection receiving energy from the rails thereof and alternatelypicked up and released in step with the on and off intervals of saidcoded track circuit energy; said system also including a source ofdirect current and a two-winding polarized stick relay at the exit endof said rear subsection, and circuits connecting one winding of saidtwo-winding polarized relay to the track rails of said rear subsectionalternately in series with said source of current when said track relayfor said one subsection is picked up and directly to the rails when saidtrack relay of said one subsection is released, said series connectionof said source and one winding of said two-winding polarized relayapplying energy to the rails of said rear subsection and operating 13said polarized armature of said two-winding polarized relay to one ofits two extreme positions; said system also including: a track relay anda source of direct current at the entrance end of said rear subsection,an impulse relay picked up only on current of a selected polarity foralternately connecting said track relay and the current source to thetrack rails at said entrance end of said rear subsection according assaid impulse relay is picked up or released, said current source poledto supply energy having a polarity effective to operate said polarizedarmature of said two-winding polarized relay to the other of its saidtwo positions, a transformer having one winding connected in circuitwith said impulse relay and having another winding, means controlled byeach release of the track relay at said entrance end of said rearsubsection for .supplying energy to said other winding of saidtransformer whereby an impulse of current of said selected polarity isinduced in said one winding and supplied to said impulse relay, meanscontrolled by said track relay at said entrance end of said rearsubsection effective when that relay ceases to operate alternatelybetween its pickedup and released positions for periodically supplyingenergy to said other winding of said transformer; said highway crossingsignal control apparatus comprising a control relay energized only whenthe armature of said two-winding polarized relay operates alternatelybetween its said one and second positions, a second relay energized overa circuit including a contact closed when said armature of saidtwo-winding relay operates to its said one position, a circuit for theother winding of said two-winding polarized relay including the backcontact of said second relay and a contact closed only when the trackrelay of the front subsection ceases to operate alternately between itspicked-up and released positions and a source of current poled to causeenergization of said second winding of said twowinding relay in such amanner as to operate said polarized armature to its said one position;and a highway crossing signal at said intersection controlled by saidcontrol relay.

5. Coded feed-back apparatus for a coded track circuit system for asection of railway track in which coded energy is applied to the trackrails at one end of the section, said apparatus comprising incombination, an impulse relay, a code responsive track relay connectedto receive energy from the track rails at the other end of said sectionwhen said impulse relay is released, a source of current connected tothe track rails at said other end of said section when said impulserelay is picked up, a decoding transformer having a primary windingsupplied with a pulse of direct current energy of one relative polarityeach time said track relay picks up and of the other relative polarityeach time said track relay releases, an impulse transformer having itssecondary winding connected to said impulse relay, a circuit connectinga secondary winding of said decoding transformer to the primary windingof said impulse transformer, said impulse relay and the secondary ofsaid impulse transformer being arranged so that the impulse relay picksup only in response to the induction of energy of a preselected polarityin said secondary winding, a coding contact operating between first andsecond positions, and a circuit including said coding contact effectivewhen said track relay ceases to respond to the coded energy supplied tothe track rails for energizing the primary winding of said impulsetransformer.

6. In a coded track circuit system for a section of railway track inwhich coded energy is applied to the rails at one end of the section,said system including an impulse relay and having a code responsivetrack relay and a source of current connected respectively to the trackrails at the other end of the track section according as said impulserelay is released or picked up respectively, said system also includinga decoding transformer having a primary winding supplied with directcurrent of one relative polarity or the other according as said trackrelay is picked up or released respectively, the combination with saidimpulse relay and decoding transformer of an impulse transformer havingits secondary winding connected to said impulse relay, a circuitconnecting a secondary winding of said decoding transformer to theprimary winding of said impulse transformer, said impulse relay andsecondary of said impulse transformer being arranged so that the impulserelay picks up only on the inducthe track relay ceases to pick up andrelease alternately in response to the coded energy supplied to thetrack rails.

7. In a coded track circuit system for a section of railway track inwhich coded energy is supplied to the track rails at one end of thesection, said system including an impulse relay and having a track relayand a source of current connected respectively to the track rails at theother end of the track section according as said impulse relay isreleased or picked up respectively, said system also including adecoding transformer having a primary winding supplied with directcurrent of one relative polarity or the other according as said trackrelay is picked up or released respectively, and also including adetecting relay connected to receive energy from said decodingtransformer and picked up only when the primary winding of thattransformer is alternately supplied with current of one relativepolarity and the other as a result of the response of the track relay tocoded energy received from the track rails, the combination with saidimpulse relay and decoding transformer of an impulse transformer havingits secondary winding connected to said impulse relay, a circuitconnecting a secondary winding of said decoding transformer to theprimary winding of said impulse transformer, said impulse relay andsecondary of said impulse transformer being arranged so that the impulseThe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,213,186 Blosser Sept. 3, 19402,332,874 Staples et a1 Oct. 26, 1943 2,335,765 Judge Nov. 30, 19432,405,860 Thompson Aug. 13, 1946

